This investigation has four objectives directed toward developing the hibernator as a model system for studying the effects of narcotics on central nervous system (CNS) function and for studying the effects of changes in the CNS associated with the hibernation state of the mechanisms underlying the development of physical dependence on and tolerance to narcotics. The first objective is to produce physical dependence on morphine administered systemically in euthermic (not hibernating) ground squirrels (Citellus lateralis) and to establish and quantitate the specific abstinence syndrome precipitated by a narcotic antagonist (naloxone). The second objective is to determine the effects of different seasons of the hibernation cycle on physical dependence on morphine, as determined by the naloxone-precipitated abstinence syndrome. The third objective is to study the effects of deep hibernation on the nature of physical dependence on morphine, as determined by the specific abstinence syndrome precipitated by naloxone. The fourth objective is to determine the effects on body temperature of systemic or intrahypothalamic injections of morphine in ground squirrels during euthermia and deep hibernation.